System for catalytic coating of a substrate

ABSTRACT

A catalyst composition is applied to an interior of a hollow substrate. The composition is coated on the substrate by immersing the substrate into a vessel containing a bath of coating slurry. A vacuum is then applied to the partially immersed substrate. The intensity of the vacuum and its application time is sufficient to draw the coating slurry upwardly from the bath into each of a plurality of channels located in the interior of the hollow substrate. After removing the substrate from the bath it is rotated 180°. A blast of pressurized air is applied at an intensity and for a time sufficient to distribute the coating slurry within the channels of the substrate to form a uniform coating profile therein.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention:

[0002] The present invention relates to an apparatus and method forcoating a substrate, and more particularly to an apparatus and methodfor impregnating monolithic substrates with a catalytic material.

[0003] 2. Description of the Prior Art:

[0004] Catalytic converters are well known for the removal and/orconversion of the harmful components of exhaust gases. Catalyticconverters have a variety of constructions for this purpose. In one formthe converter comprises the rigid skeletal monolithic substrate on whichthere is a catalytic coating. The monolith has a honeycomb-typestructure which has a multiplicity of longitudinal channels, typicallyin parallel, to provide a catalytically coated body having a highsurface area.

[0005] The rigid, monolithic substrate can be fabricated from ceramicsand other materials. Such materials and their construction aredescribed, for example, in U.S. Pat Nos. 3,331,787 and 3,565,830 each ofwhich is incorporated herein by reference. Alternatively, the monolithscan be fabricated from metal foil.

[0006] The monolithic substrate and particularly the multiplicity ofchannels can be coated with a slurry of a catalytic and/or absorbentmaterial.

[0007] One method of coating a prefabricated monolithic substrate is topump the catalyst slurry into the respective channels and then subjectthe coated substrate to a drying operation. Such systems have beenunsuccessful in providing a uniform coating thickness and a uniformcoating profile wherein the catalyst coating is deposited over the samelength of each of the channels.

[0008] It has been proposed to employ a vacuum to draw the catalystslurry upwardly through the channels. For example, Peter D. Young, U.S.Pat. No. 4,384,014 discloses the creation of a vacuum over themonolithic substrate to remove air from the channels and then drawingthe catalyst slurry upwardly through the channels. The vacuum is thenbroken and excess slurry is removed, preferably by gravity drainage.

[0009] James R. Reed, et al., U.S. Pat. No. 4,191,126, discloses thedipping of the monolithic substrate into a slurry and then utilizingsubatmospheric pressure to purge the excess coating slurry from thesurfaces of the support. The applied vacuum is intended to unplug thechannels so that the slurry is drawn over the surfaces of each of thechannels.

[0010] An improvement in these systems is disclosed in Thomas Shimrock.et al., U.S. Pat. No. 4,609,563. This system encompasses a method ofvacuum coating ceramic substrate members with a slurry of refractoryand/or catalyst metal components wherein precisely controlled,predetermined amounts of the slurry are metered for application to theceramic monolithic substrate. The monolithic substrate is lowered into avessel, also known as a dip pan, of preferably predetermined dimensionsto a predetermined depth containing the precise amount of slurry whichis to be coated onto the substrate. The slurry is then drawn up by avacuum which is applied to the end of the substrate opposite to the endwhich is immersed in the bath. No draining or purging of excess coatingslurry from the substrate is necessary nor is any pre-vacuum applicationstep required to eliminate air.

[0011] A further improved method is disclosed Victor Rosynsky et al, inU.S. Pat. No. 5,866,210 entitled, “METHOD FOR COATING A SUBSTRATE.”There is disclosed a vacuum infusion method for coating monolithicsubstrates in which each of the channels comprising the substrate iscoated with the same thickness of the coating and is characterized by auniform coating profile wherein each channel of the substrate is coatedover the same length. In particular, the method is directed to a vacuuminfusion method for coating a substrate having a plurality of channelswith a coating media comprising:

[0012] a) partially immersing the substrate into a vessel containing abath of the coating media, said vessel containing an amount of coatingmedia sufficient to coat the substrate to a desired level withoutreducing the level of the coating media within the vessel to below thelevel of the immersed substrate;

[0013] b) applying a vacuum to the partially immersed substrate at anintensity and a time sufficient to draw the coating media upwardly fromthe bath into each of the channels to form a uniform coating profiletherein; and

[0014] c) removing the substrate from the bath.

[0015] Optionally, after the coating media is applied to the substrateand as the substrate is being removed from the bath, a vacuum continuesto be applied to the substrate at an intensity equal to or greater thanthe intensity of the vacuum imposed on the partially immersed substrate.After the vacuum is imposed, the substrate is inverted and coated froman opposite end producing two coatings having uniform coating profiles.This procedure is known to reduce the overlap of the coating media.

[0016] Overlap of the coating compound is particularly problematic tothe automobile industry. The overlap area increases the delta pressureacross the catalyst converter which adversely impacts engine performanceand fuel consumption and increases the engine's wear. Equallyproblematic is where the coating compound has a gap in the middle whichresults from incomplete coverage during the coating procedure. This,too, may adversely affect converter and engine performance. However,where the substrate is inverted in order to coat both ends, it isextremely difficult to ensure that the coating materials will notoverlap or gap to some extent. Even the smallest amount of overlap orgap negatively affects catalytic performance.

[0017] It would therefore be a significant benefit in the art of coatingmonolithic substrates and particularly monolithic substrates for use incatalytic converters if each channel can be coated with the samethickness of coating for the same length without any overlap or gap inthe coating materials.

SUMMARY OF THE INVENTION

[0018] The present invention provides a system for applying a catalystcomposition to an interior of a hollow substrate which eliminates theoverlap or gap of the coating slurry. Generally stated, the systemcomprises coating a substrate with a catalyst composition by immersingthe substrate into a vessel containing a bath of coating slurry andapplying a vacuum to the partially immersed substrate at an intensityand time sufficient to draw the coating slurry upwardly from the bathinto each of a plurality of channels located in the interior of thehollow substrate; removing the substrate from the bath: rotating thesubstrate 180°; and applying a blast of pressurized air to the substrateat an intensity and time sufficient to distribute the coating slurrywithin the channels of the substrate to form a uniform coating profiletherein.

[0019] The term “uniform coating profile” as used herein means that eachchannel of the substrate will be coated over the same length.Advantageously, the present invention provides a system whereby theoverlap or gap of the catalytic composition on the substrate iscompletely eliminated. This provides distinct advantages for catalyticconverters. First, less precious metal may be used because the catalyticcomposition is evenly distributed throughout the substrate. Second,there is more precise control over the placement of the catalyst whichis particularly advantageous when using multiple catalyst coatingcompositions. Third, by virtue of removing the overlap or gap, thethickness of the coating can be more precisely controlled, particularlyin multi coating applications. Resistance to the flow of gases to betreated through the substrate is thereby reduced, resulting in bettercontrol over and less severe pressure drops through the channels. Whensuch substrates are used as catalytic converters, engine performance isnot diminished. As used herein the term “vacuum infusion” shallgenerally mean the imposition of a vacuum to infuse a coating slurryinto a plurality of channels within a monolithic substrate.

[0020] In another aspect of the present invention there is provided amethod for applying a catalyst composition to the interior of a hollowsubstrate comprising coating the interior of a hollow substrate with apredetermined amount of a catalytic composition; rotating the substrate180°; and applying a blast of air to the substrate to distribute thecatalytic composition therewithin. Catalytic converters produced inaccordance with the present invention exhibit less wet gain and preciousmetal variability, resulting in increased production output and lessexpense incurred from the use of precious metals. Advantageously,automobiles using these materials have reduced fuel consumption becausethere is much lower pressure drop across the catalyst, than is seen withcatalytic converters having an overlap or gap of the catalyticcomposition.

[0021] The present invention also provides an apparatus for coating asubstrate with a catalytic composition. The apparatus comprises acoating station comprising a dip pan containing a continuous supply of acoating slurry, a vacuum cone operatively engaged to apply a vacuum tothe substrate, an inflatable bladder clamp for supporting and rotatingthe substrate and an air blast station for supplying a blast ofpressurized air to the substrate. The apparatus may further comprise amovable platform for moving the substrate between stations and a robotfor automatically loading and unloading the substrate onto and off ofthe apparatus. Advantageously, the apparatus is highly automated andefficient, making it less expensive and more reliable to use than priorart apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention will be more fully understood and furtheradvantages will become apparent when reference is had to the followingdetailed description and the accompanying drawings, in which:

[0023]FIG. 1 is a schematic flow diagram of the system illustrating theapplication of a low and high intensity vacuum to a substrate, 180°rotation of the substrate, and the application of an air blast;

[0024]FIG. 2 is a side elevation view illustrating the coating stationwith the vacuum hood lowered about a substrate immersed in the dip pan;

[0025]FIG. 3 is a top view of an inflatable bladder clamp in accordancewith the present invention;

[0026]FIG. 4 is a top view of a robotic arm for loading and unloading asubstrate;

[0027]FIG. 5 is a side elevation view of an air blast station inaccordance with the present invention;

[0028]FIG. 6 is a front elevation view of an air blast station adaptedto accommodate two monolithic substrates:

[0029]FIG. 7 is a top view showing a five-station system including twoweigh stations; one interposed between the loading/unloading station andthe coating station, the other interposed between the air blast stationand the loading/unloading; and

[0030]FIG. 8 is a side elevation view of a weigh station in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention is directed to an improved system forcoating a catalytic composition onto a substrate whereby the catalyticcomposition is uniformly coated within the interior surface of thesubstrate. The system of the present invention combines vacuum infusioncoating with an air blast apparatus to provide a uniformly coatedsubstrate without gaps or overlap of the catalytic composition withinthe interior of the substrate. As a consequence of the presentinvention, production output is increased and less precious metal isrequired in the catalytic composition, making a higher quality catalystsless expensive to produce. Moreover, automobiles using the catalysts ofthe present invention exhibit reduced fuel consumption, making thesematerials much more attractive to the automobile industry.

[0032] More specifically, the system of the present invention comprisescoating a substrate with a catalyst composition by immersing thesubstrate into a vessel containing a bath of coating slurry and applyinga vacuum to the partially immersed substrate at an intensity and timesufficient to draw the coating slurry upwardly from the bath into eachof a plurality of channels located in the interior of the hollowsubstrate; removing the substrate from the bath; rotating the substrate180°; and applying a blast of pressurized air to the substrate at anintensity and time sufficient to distribute the coating slurry withinthe channels of the substrate to form a uniform coating profile therein.

[0033] Referring to FIG. 1 of the drawings, there is shown a schematicdiagram of a system embodying the principles of the present invention.Generally stated, a monolithic substrate 21 is immersed in a catalyticcomposition, a low intensity vacuum applied, the substrate is removedfrom the coating slurry, and a higher intensity vacuum applied.Thereafter, the substrate is rotated 180° and an air blast is applied.This is accomplished by a coating station and an air blast station whichmay simultaneously coat one, two, or more substrates. The system may bedesigned to allow a human operator to manually move the substratebetween stations, or, alternatively, with a moveable platform whichadvances the substrate between stations (discussed in more detailbelow). In this instance, an electrical motor drives the moveableplatform.

[0034] The process of providing the coated catalytic substrate isbriefly described as follows: The operator defines system parameters(i.e., depth of immersion of the substrate in the coating slurry,duration and intensity of the vacuum and air blast, length of time ateach indexing station. etc.), adjusts the system to conform with thespecified parameters and presses a start button on a control panel (notshown). A robot or human operator picks up a hollow substrate which isopen at both ends and transfers this to a bladder clamp which inflatesto seal the periphery of substrate and hold the substrate in place. Thebladder clamp is connected to a platform which serves to move thesubstrate between different stations within the system. Where a humanoperator moves the substrate between the stations, each of the differentstations has its own bladder clamp to secure the substrate. Assumingthat a movable platform is used, the platform advances the inflatedbladder clamp to the coating station where the dip pan moves upward to apredetermined height causing the substrate to immerse to a given depth.A low vacuum is applied to draw a slurry up through the interior of thesubstrate from the dip pan. The substrate is then lifted out of the dippan, a high vacuum applied, and the substrate rotated 180°. At thispoint, the substrate and the platform advances to an air blast stationwhere the upper and receiving hood of the air blast station close aroundthe substrate, and a blast of air is applied to the substrate todistribute the coating slurry about the uncoated portions of thesubstrate. After the air blast, the upper and receiving hoods of the airblast station open and the bladder clamp and the platform advances to aloading/unloading station where the bladder clamp deflates and thesubstrate is removed from the system.

[0035] While the overall system is generally illustrated in FIG. 1, itcan be better understood by referring to a number of stations which makeup the entire system. Of course, each of these stations may be adaptedwith computerized controls to provide for automatic action once thesystem is initially programmed by an operator. A suitable apparatus forcoating substrates in accordance with the present invention ismanufactured by MPT Technologies Inc. of Brecksville, Ohio. Turning nowto FIG. 2, there is shown a perspective view of a coating stationutilized by the present invention. Generally stated, coating station 11comprises a vacuum which is supplied via vacuum pump 18 through a line10 to a vacuum hood 12 which is operatively connected to the substratewhen the substrate in placed in contact with the coating slurry. A dippan 14 holds continuously circulating coating slurry received from astorage tank for coating the substrate. In accordance with the presentinvention, an inlet tube provides for the continuous flow of coatingslurry from a slurry tank (not shown) to the dip pan 14. An outlet tubeprovides for the continuous flow of coating slurry out of the dip pan toa slurry recovery tank (not shown). In this way, the coating slurry maybe recovered and recycled back into the dip pan 14 thereby reducing thecost associated with furnishing fresh coating slurry into the system. Aseries of valves may be located on the inlet and outlet tubes toregulate the slurry flow. The coating slurry need not be metered toprovide an exact amount of coating slurry to the dip pan 14. Instead, acontinuous flow of coating slurry is provided to the dip pan 14.Preferably, the dip pan 14 is configured with a U-shaped receptaclewhich is contiguous with the circumference of the dip pan 14 andfunctions to catch and direct any slurry overflow to the outlet tube.The dip pan 14 is operatively connected to a carriage driven by a servomotor which functions to raise and lower the dip pan 14 along thevertical axis to immerse the substrate 21 therein or remove ittherefrom. A computer controls the vertical movement of the dip pan 14to control the depth of immersion of the substrate 21 in the coatingslurry to insure an adequate volume 22 of the coating slurry is suppliedto the dip pan to coat the end of the substrate 21 immersed therein. Thevolume of coating slurry required to coat the substrate 21 in accordancewith the present invention is based upon a variety of factors well knownin the art including volume of the substrate, required slurry loading,viscosity of the slurry, etc.

[0036] The dimensions and shape of the dip pan 14 may be varied over awide range. A single size and shape dip pan may be used to coat a widevariety of different size and shape monolithic substrates. Thus, the dippan 14 is capable of accommodating a rectangular substrate as well asoval, polygon, and circular substrates which may be used from time totime for special applications.

[0037] Where the apparatus utilizes a platform to advance the substratebetween stations, the apparatus may further comprise a loading/unloadingstation. As is shown in FIG. 3, the loading/unloading station consistsof a bladder clamp 400 which has a larger circumference than thesubstrate. The bladder clamp 400 is equipped with an air supply inlet(not shown) which enables the bladder to inflate so that the interior407 sealingly engages the outside perimeter of a substrate. The bladderclamp 400 is also equipped with an air supply outlet that allows thebladder to deflate when necessary. Preferably, the air supply inlet andoutlet are the same. Each of these inlets and outlets may be computercontrol led to permit automatic inflation and deflation of bladder clamp400. Bladder clamp 400 is permanently affixed to the moveable platformby suitable means such as screws, pins, clamps, or the like. The bladderclamp 400 serves to move the substrate between the different stations ofthe apparatus. It is contemplated that any shape and type of bladderclamp may be used so long as it accommodates the shape of the substrate.By use of a bladder clamp, the apparatus can coat any substrate,regardless of shape of size. Of course, the apparatus need not utilize arobot and the associated loading/unloading station. Instead, a humanoperator can manually move the substrate between the different stations.In an alternative embodiment, the loading and unloading stations may beseparate, each having the inflatable bladder clamp described above.

[0038] The bladder clamp is also connected to a rotational device whichserves to rotate the substrate 180°. Any rotational device may be used,however, a pneumatically actuated rotational device is preferred. Onesuch example of a preferred rotational device is manufactured by ShunkCorp. of Germany.

[0039] A robot may be used to load and unload the substrate to and fromthe apparatus. FIG. 4 illustrates a top view of a robotic arm which maybe used in the present invention. Any type of robotic apparatus which isdesigned to move objects may be used. A particularly suitable robot issold by Adept Corp. of Cincinnati, Ohio. As can be seen, the robot 300is capable of grasping the substrate and thereby move it via movable arm302 to and from the apparatus. While robot 300 is shown adapted withpinchers 301, any end unit suitable for grasping substrates used forcatalytic converters may be used. Robot 300 may also be adapted with avision system which allows robot 300 to properly orient the substrate inthe loading station. Robot 300 may also be used to remove the coatedsubstrate from the apparatus. That is, once the substrate has beencoated and subjected to an air blast, the moveable platform advances tothe load/unload station where the robot 300 grasps the coated substratefrom the bladder clamp 400.

[0040] Referring to FIG. 5 of the drawings, there is shown a sideelevation view of the air blast station 12 utilized in the system of thepresent invention. A suitable unit for performing the air blast inaccordance with the present invention is manufactured by MPTTechnologies Inc. of Brecksville, Ohio. The air blast station generallyincludes upper hood 200, receiving hood 201, air supply 207, andstationary frame structure 213. Air blast feed 205 is connected to thetop 204 of upper hood 200 on one end and serves to provide a source ofpressurized air to upper hood 200. The top of air blast feed 205 isthreadingly engaged with line 206. The top 204 of upper hood 200 is alsoconnected to carriage 203 for movement along rod 216 on the vertical orZ axis. Carriage 203, is in turn, coupled to stationary frame structure213. A servo motor (not shown) appropriately drives carriage 203 up anddown along the vertical axis which operate to open and close upper hood200 and attached air blast feed 205. Line 206, which may be made of anysuitable material to carry pressurized air, runs between the air blastfeed 205 and air supply 207.

[0041] Receiving hood 201 is adapted to receive the substrate. Slurrydischarge tube 209 extends from an aperture 208 positioned at the bottomof receiving hood 201. On the opposite end, slurry discharge tube 209 iscoupled to an aperture 210 positioned on the top of slurry recovery tank211. Slurry recovery tank 211 may be connected to slurry tank 34 of thecoating station via piping and an optional servo motor connected to thesystem to drive the used catalytic composition from slurry recovery tank211 to recovery tank 34 for reuse in the system. Receiving hood 201 iscoupled to a carriage (not shown) which provides for movement ofreceiving hood 201 in the vertical or Z direction when driven by a servomotor to open and close the receiving hood. In the closed position,upper hood 200 sealingly engages one side of bladder clamp 400 and thereceiving hood 201 sealingly engage with the other side of bladder clamp400 to form a seal which can contain, as discussed below, filled withpressurized air from air supply 207. In the open position, upper hood200 is sufficiently distanced from receiving hood 201 to allow forloading or unloading of the substrate.

[0042] Air supply 207 is contained within a tank, typically made ofmetal, plastic or other material suitable to hold pressurized air. Thetank may be refillable, that is, it may be exchanged for a new tank whenthe contents have been used, or it may be connected to another airsupply which provides the air for refill in air supply 207. Anadjustable regulator (not shown) is attached to air blast station 12 inorder to adjust the pressure in air supply 207. As previously mentioned,line 206 connects air supply 207 with air blast feed 205, and therebyprovides a passageway for air to travel from air supply 207 to upperhood 200. A normally open feed valve 215 is suitably mounted on airsupply 207 and operates on line 206 to regulate the flow of air into airblast feed 205. Thus, when a substrate is placed on receiving hood 201and upper hood 200 is closed to sealingly engage receiving hood 201, airsupply 207 provides a regulated air supply via valve 215 and line 206 toair blast feed 205 which, in turn, provides a pressurized air to thecavity formed when upper hood 200 is in the closed position. Thispressurized blast of air serves to uniformly distribute the coatingmaterial throughout in the interior of the substrate and “blow off” theexcess. The excess coating slurry enters slurry recovery tank 211 by wayof gravity feed from slurry discharge tube 209 via aperture 210.

[0043]FIG. 6 illustrates a front elevational view of an air blaststation in accordance with the present invention adapted tosimultaneously receive and provide a blast of air to two coatedsubstrates. In this illustration, an upper hood is represented by 220,receiving hood by 221, stationary frame structure by 243, and air blastfeed and its associated carriage as 225 and 223, respectively. Line 226connects air blast feed 225 to the air supply (not shown). Excesscoating slurry, which has been “blown off” the substrate after the airblast is captured by slurry recovery tank 230 via slurry discharge tube229.

[0044] The apparatus may also be equipped with weighing stations forweighing the substrate before coating and after the air blast. Byweighing the substrate before and after coating, the percentage of wetgain variability, that is the uniformity of the coating process, can bedetermined. FIG. 7 provides a top view of a five-station automaticapparatus in accordance with the present invention withloading/unloading station 401, weigh station 402, coating station 403,air blast station 404, and weigh station 405. FIG. 8 illustrates a weighstation used for simultaneous weighing of two substrates in accordancewith the present invention. Generally stated, the weigh station isconfigured so that when the moveable platform advances to the station,the bladder clamp deflates. Below the platform is positioned a unitcontaining scale 501 and a servo motor 502 supported by stationary frame504 which operates via rod 503 to raise and lower the scale in avertical direction along the Y axis. When scale 501 is raised upward, ittouches the bottom of the substrate, enabling weighing of the uncoatedor coated substrate. After performing weight calculations, scale 501lowers along rod 503. Where weight calculations are performed prior tocoating, the substrate is made to rest on the weigh platform which actsas a register platform to determine the vertical location of thesubstrate. Advantageously, the vertical location of the substrate ascalculated at the weigh station may be used in the coating station todetermine the depth of immersion of the substrate into the slurry. Theweigh station is connected to an electronic means which records theweight of the substrates. As with the other stations described herein,the weigh station may be adapted with at least one computer to performany of the foregoing functions.

[0045] In accordance with the method aspect of the present invention, asdescribed above, a human operator programs system parameters into acomputer prior to commencing operation. Once programmed, the systemautomatically continues the coating process until operations areterminated or redefined by the operator. A robot or a human operatormanually places the uncoated substrate in the loading/unloading station13 where bladder clamp 400 inflates to hold the substrate securely inplace, and the moveable platform advances the substrate to the coatingstation 11.

[0046] The coating procedure used in the present invention is broadlydescribed by Victor Rosynsky et al., U.S. Pat. No. 5,866,210, which isexpressly incorporated herein by reference. This procedure is modifiedin the present invention as described below. When the substrate advancesto the coating station, dip pan 14, which contains a continuous supplyof coating slurry, raises to contact the underside of the inflatedbladder clamp in accordance with a prescribed depth. As previouslyindicated, this is determined based upon a variety of factors such asvolume of the substrate, required slurry loading, and viscosity ofslurry, etc. The vacuum hood moves downward to sealingly engage one sideof the bladder clamp and the raised dip pan sealingly engages the otherside of the bladder clamp. In this way, a sealed cavity is formed.

[0047] When the substrate is placed into the coating slurry, the coatingslurry is drawn upwardly into the interior channels through capillaryaction even without the imposition of a vacuum. Because there issufficient volume of the coating slurry above the immersed end of thesubstrate, capillary action is uniformly provided to all of thechannels. As a result, a uniform coating profile can be initiallyobtained even in the absence of a vacuum. Nevertheless, it is necessaryto impose a low intensity vacuum to further draw the coating slurryupwardly.

[0048] The low intensity vacuum should be maintained at no more thanabout 1 inch of water. If the vacuum exceeds this level, the consistencyof the length and thickness of the coating may be compromised. The timethe low intensity vacuum is applied will vary depending on theconsistency and density of the coating slurry and the length thechannels to be coated. In most cases, the low intensity vacuum will beapplied for from about 1 to 3 seconds. Advantageously, the seal betweenthe substrate periphery and the interior of the bladder clamp enhancesthe movement and overall uniformity of the coating slurry in thechannels. As previously indicated, a second vacuum operation of the sameor higher intensity (i.e., greater than 1 inch of water, typically fromabout 5 to 15 inches of water) can be applied after the vacuum hood israised and the substrate has been removed from the coating slurry. Theduration of the second vacuum operation is typically from about 2 to 4seconds. In most cases the vacuum operation(s) (i.e., the sum of thefirst and second vacuum operations) will last for no more than a totaltime of about 5 seconds. The substrate is then rotated 180° in thebladder clamp and indexed to the air blast station 12.

[0049] When the platform reaches the air blast station 12, upper hood200 is lowered and receiving hood 201 raised to sealingly engaged withupper hood 200 to form a cavity in which the substrate is positioned. Ablast of air, typically pressurized between about 20 to about 50 psi isdelivered to the substrate via line 206. The duration of the air blastranges from about 0.3 to about 0.5 seconds, and is typically about 0.3seconds. After the air blast, upper hood 200 is raised, the lower hoodlowers, and the platform advances to the load/unload station wherebladder clamp 400 deflates and a robot or human operator removes thesubstrate. As previously discussed, weigh stations may be interposedbefore the coating station and after the air blast station.

[0050] Any monolithic substrate can be coated in accordance with thepresent invention. Such substrates are comprised of fine, parallel gasflow extending therethrough form an inlet face to an outlet face of thesubstrate so that the channels are open to air flow entering from thefront and passing through the substrate and out the rear. Preferably,the channels are essentially straight from their inlet to their outletand are defined by walls in which a coating slurry is coated as a washcoat so that the gases flowing through the channels contact the coatingslurry. The flow channels are thin wall channels which can be of anysuitable cross-sectional shape and size such as trapezoidal,rectangular, square, sinusoidal, hexagonal, oval, circular or formedfrom metallic components which are corrugated and flat as are known inthe art. Such structures may contain from about 60 to 1200 or more gasinlet openings (“cells”) per square inch of cross section. Suchstructures are disclosed for example in U.S. Pat. Nos. 3,904,551;4,329,162; and 4,559,193, each of which are expressly incorporatedherein by reference.

[0051] Coating slurry which may be coated in accordance with the presentinvention can vary widely and include, but are not limited to catalystcompositions, absorbent compositions and combinations thereofcustomarily used for the production of catalytic converters. Multiplecoats of different compositions may also be used. Suitable coatingslurry compositions are as disclosed for example in U.S. Pat. Nos.5,057,483: 4,714,694; and 4,134,860, each of which is expresslyincorporated herein by reference.

[0052] After the substrate has been removed from the system it may bedried before the substrate is sent to a heating section where thecoating is cured. Drying of the coated substrate can be conducted in anysuitable manner which may be facilitated by the imposition of a vacuum.A particularly suitable drying process is described in copendingapplication U.S. Ser. No. 09/067,831 filed Apr. 28, 1998, entitled“Method for Drying a Coated Substrate,” attorney docket number 3924, thecontents of which are expressly incorporated herein by reference.

[0053] In accordance with the present invention, a substrate may becoated within about 5 to about 10 seconds, even where weigh stations areemployed. The amount of dwell time at a single station can vary, andwill depend upon coating type, coating thickness, and the like. With a10-second cycle, single and double coating apparatus may thus coatapproximately 360 substrates/hour and 720 substrates/hour, respectively.Likewise, a 5-second cycle will enable the coating of 1420substrates/hour, making the method extremely efficient. The substratesare uniformly coated, without any of the gaps or overlay present in theprior art methods which require that when opposite ends of the substrateare dipped in the coating slurry. Moreover, substrates coated inaccordance with the present invention exhibit lower wet gain andprecious metal variability, which demonstrates the reliability and therelatively lower expense of the present invention. For example, prior tothe present invention, the wet gain variability between coatedsubstrates was approximately 10-15%. Substrates produced in accordancewith the method described herein, by contrast, evidence only about 2.6%wet gain variability. Similarly, prior to the present invention, thetotal precious metal gradient within a substrate was about 10-20%, whilesubstrates produced as described herein exhibit less than 5% preciousmetal gradient. As such, precious metal is evenly distributed throughoutthe substrate, thereby providing controlled precious metal loading.

[0054] Having thus described in invention in rather full detail, it willbe recognized that such detail need not be strictly adhered to but thatvarious changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the invention, as defined bythe subjoined claims.

1. A system for applying a catalyst composition to an interior of ahollow substrate comprising: coating a substrate with a catalystcomposition by immersing the substrate into a vessel containing a bathof coating slurry and applying a vacuum to the partially immersedsubstrate at an intensity and time sufficient to draw the coating slurryupwardly from the bath into each of a plurality of channels located inthe interior of the hollow substrate; removing the substrate from thebath; rotating the substrate 180°; and applying a blast of pressurizedair to the substrate at an intensity and time sufficient to distributethe coating slurry within the channels of the substrate to form auniform coating profile therein.
 2. A system as recited in claim 1,wherein after the substrate has been removed from the bath, a vacuum isapplied to the substrate.
 3. A system as recited in claim 2, wherein theintensity of the vacuum applied after the substrate has been removedfrom the bath is at least equal to the intensity of the vacuum appliedto the substrate while immersed in the bath.
 4. A system as recited inclaim 1, wherein the air blast station comprises an upper hood, areceiving hood and an air supply operatively connected to the upperhood.
 5. A system as recited in claim 1, wherein the duration of the airblast ranges from about 0.3 to about 0.5 seconds.
 6. A system as recitedin claim 1, wherein the air blast is pressurized between about 20 toabout 50 psi.
 7. An apparatus for applying a catalyst to the interior ofa hollow substrate comprising: a coating station comprising a dip pancontaining a coating slurry, a vacuum cone operatively engaged to applya vacuum to the substrate; and an air blast station for supplying ablast of pressurized air to the substrate.
 8. An apparatus as recited inclaim 7, further comprising a platform which is movable between thecoating station and the air blast station.
 9. An apparatus as recited inclaim 8, further comprising a station for loading and unloadingsubstrate.
 10. An apparatus as recited in claim 9, further comprising arobot for placing and removing the substrate from the loading andunloading station.
 11. An apparatus as recited in claim 8, furthercomprising an inflatable bladder clamp affixed to the platform.
 12. Anapparatus as recited in claim 11, further comprising a rotationaldevice.
 13. An apparatus as recited in claim 7, further comprising aprogrammable computer for defining system parameters.
 14. An apparatusas recited in claim 7, wherein the air blast station comprises an upperhood, a receiving hood, and an air supply operatively connected to theupper hood.
 15. An apparatus as recited in claim 9 further comprising atleast one station for weighing the substrate.
 16. An apparatus asrecited in claim 15, wherein one station for weighing the substrate islocated between the loading/unloading station and the coating station,and another station for weighing the substrate is located between theair blast station and the loading/unloading station.
 17. A method forapplying a catalyst composition to the interior of a hollow substratecomprising: coating the interior of a hollow substrate with a catalyticcomposition: rotating the substrate 180°; and applying a blast of air tothe substrate to distribute the catalytic composition therewithin.
 18. Amethod as recited in claim 17, further comprising loading the substrateinto an inflatable bladder clamp.
 19. A method as recited in claim 18,wherein the substrate is loaded into the inflatable bladder clamp by arobot.
 20. A method as recited in claim 17, further comprising dryingthe substrate.
 21. A method as recited in claim 17, wherein the airblast is supplied for a duration ranging from about 0.3 to about 0.5seconds.
 22. A method as recited in claim 17, further comprisingweighing the substrate.